Monoclonal antibodies provide powerful diagnostic and therapeutic tools for treatment of a variety of disease, e.g., cancer. However, use of monoclonal antibodies is limited due to immunogenicity. In order to ameliorate these effects, humanization strategies have been devised that replace portion of the monoclonal antibodies with human counterparts.
Current techniques for humanizing antibodies involve selecting the complementarity determining regions (CDRs), i.e., the antigen binding loops, from a donor monoclonal antibody, and grafting them onto a human antibody framework of known three dimensional structure (see, e.g., WO98/45322; WO 87/02671; U.S. Pat. Nos 5,859,205; 5,585,089; 4,816,567; EP Patent Application 0173494; Jones, et al. (1986) Nature 321:522; Verhoeyen, et al., (1988) Science 239:1534 Riechmann, et al. (1988) Nature 332:323; and Winter & Milstein, (1991) Nature 349:293) or performing database searches to identify potential candidates. In a typical method aided by computer modeling and comparison to human germline sequences, the antigen binding loops of the monoclonal antibody to be humanized are superimposed onto the best fitting frameworks. This allows the identification of framework residues that are potentially important for the affinity of the antibody.
Humanization efforts are limited, however, by the number of human frameworks available. This invention meets the need for additional human framework sequences and provides methods of providing stable human framework sequences for specificity graftings, and in some embodiments, methods of modifying the sequences to generate stable humanized antibodies.